Ono doubt this news raised some questions. What is mad cow disease again and how do you recognize it in cows? What does such a positive case mean for us? Although it has already been confirmed that this is an isolated case and that there is no outbreak, it is still useful to refresh the knowledge about this disease.
What is it?
Mad cow disease – also known as bovine spongiform encephalopathy (BSE) – is a disease that occurs in cattle and belongs to the group of ‘transmissible spongiform encephalopathies’ (TSE). As the name suggests, BSE causes spongy brain abnormalities.
BSE is caused by a misfolded protein in the body, otherwise called a ‘prion’. Unlike the normal protein variant, these prions can no longer be broken down and will therefore accumulate in the brain tissue. Because of this accumulation, nerve cells die and in this way make holes in the brain. These prions can arise spontaneously (atypical BSE), be passed on through infected BSE material (typical BSE), or can be the result of a mutation in the genes encoding these proteins.
Symptoms
Once an animal is infected with prions, it takes an average of 5 years for this animal to show symptoms. BSE can be recognized in ruminants by various symptoms that worsen over time. This starts with, among other things, hypersensitivity to stimuli (such as tactile stimuli on the skin or sound stimuli), which is often noticeable by small muscle tremors. This hypersensitivity will gradually increase, as a result of which the animals will panic more quickly and eventually show aggressive behaviour.
In a further stage, brain damage in animals with BSE will manifest itself in neurological symptoms, such as movement disorders and paralysis, ultimately resulting in the death of the animal. To date, there is no treatment or vaccine available against BSE.
Relevance to humans
BSE is a zoonosis, which means that it is a disease that can be transmitted from animals to humans. Mad cow disease is associated with the variant Creutzfeldt-Jacob disease (vCJD), which is also part of the TSE group. VCJD is a rare brain disease that, like BSE, causes behavioral and movement disorders after a very long incubation period of several years. There is no treatment for this either, which means that the disease always has a fatal outcome.
Humans can contract this disease by eating BSE-contaminated beef (mainly brain and nerve tissue). It is therefore obvious that strict control of cattle is necessary in order to detect this disease and to prevent infected animals from entering the food chain.
Back in time
BSE was first identified in Britain in 1986. It is believed that it originated from a spontaneous mutation and that the disease was then spread in domestic livestock by feeding ruminants with meal from other infected ruminants. Such animal meal was used as a source of protein in the diet. The major outbreak, which led to more than 180,000 confirmed BSE cases in Britain at the time, led to a European ban on the feeding of mammalian meal to ruminants. Due to the risk of animal meal being carried over from non-ruminant feed to ruminant feed, a general ban was introduced at the beginning of 2001 on the use of almost all processed animal proteins in the feed of all farm animals (total feed ban).
In Belgium, BSE was first diagnosed in 1997. The last confirmed BSE-infected animal in Belgium dates from 2006. The strong decrease in the number of confirmed BSE cases, not only in Belgium but worldwide, is the result of relevant legislation with strict succession. As a result, Belgium acquired the status of ‘negligible BSE risk’ in 2012.
Control measures in Belgium
As already mentioned, there is currently no vaccine available and no treatment. Therefore, only preventive measures can be used to get this disease under control. In addition, the diagnosis of BSE cannot be performed on the live animal because brain or nerve tissue is required for this. Euthanasia or slaughter of the animal is therefore necessary to make a definitive diagnosis.
Belgium, like the other EU Member States, implements the European BSE control programme, which is based on 3 pillars: the removal of specific risk tissues from the food chain, a general ban on the use of animal protein in cattle feed and the implementation of an annual testing program in cattle, sheep and goats.
Remove risk tissue In infected cattle, the infectious prions concentrate almost entirely in the brain and spinal cord, and to a very limited extent in the tonsils and in certain nerve nodes of the intestinal tract. This so-called specified risk material (SRM) is completely removed from the human and animal food chain, both in the slaughterhouse with healthy slaughter cattle and by processing and complete incineration of carcasses of both ruminants and non-ruminants. Removing GRM from the food chain is the most important measure for protecting public health.
Feed ban The ban on feeding animal protein to farmed animals should avoid spreading the disease between ruminants. Initially there was only a ban on feeding animal meal to ruminants, but that ban was later extended to all farm animals. Breaking the cycle of feeding meat-and-bone meal from potentially BSE-infected animals to newly susceptible animals has greatly reduced the number of new cases of this disease. The feed ban is still in effect.
Monitoring program To monitor the current BSE situation in the EU, an annual monitoring program is carried out. Initially, very intensive tests were carried out. However, these rules were later relaxed because the risk has become smaller. In Belgium, healthy cattle for slaughter are no longer subject to a rapid test. The annual surveillance program now focuses entirely on cattle at risk, in particular dead cattle older than 48 months and any animal older than 48 months that undergoes emergency slaughter outside the slaughterhouse (and is therefore intended for human consumption). In our country, 26,000 BSE tests are still carried out every year. The recent BSE case in the Netherlands was detected through the testing program on fallen cattle.
It is also important to monitor the occurrence of the disease in our country. For this purpose, clinically suspected cattle are examined for BSE and these animals do not end up in the food chain. When BSE cannot be ruled out with certainty, the animals suspected of having BSE are euthanized and tested.
If BSE is suspected
Finally, just as recently in the Netherlands, a large number of measures will be taken after a suspicion and/or confirmation of BSE. The holding from which the animal originates will be placed under surveillance and the animals that could be infected by or simultaneously with the affected animal will be identified. The feeds are also identified in order to exclude them as a possible source of BSE. However, due to the very long incubation period of BSE, a direct link with the animal feed is very difficult to establish.
Atypical case
The Dutch authorities have since confirmed that the detected positive BSE case is indeed an atypical form of BSE. Such an atypical form occurs spontaneously in mainly older animals (an ‘age variant’). This means that this animal did not ingest any contaminated feed, but that the prion originated through a spontaneous mutation in the body of the cow.
This animal was destroyed, did not enter the food chain and therefore does not pose a threat to humans. This case proves that the current rules in force ensure correct, safe and efficient monitoring of BSE.
Conclusion
BSE is a disease affecting the bovine central nervous system caused by misfolded proteins known as prions. This disease can be transmitted to humans through contaminated meat and causes the variant ‘Creutzfeldt-Jacob disease’. Both in our ruminants and in humans, there is neither a vaccine nor a treatment and the outcome is fatal.
The recently discovered case in the Netherlands turned out to be a rare sporadic variant of BSE. The necessary measures for this case have been taken and in addition there is in any case a whole set of measures of active surveillance of this disease.